A conventional television system, such as a system in accordance with the NTSC broadcast standard adopted in the United States and elsewhere, processes a television signal representative of an image with a 4:3 aspect ratio (the ratio of the width to the height of a displayed image). Recently, there has been interest in using higher aspect ratio images for television systems, such as 5:3, 16:9 and 2:1, since such higher aspect ratios more nearly approximate or equal the aspect ratio of the human eye compared to the 4:3 aspect ratio of a standard television display. An advanced television system for producing 5:3 aspect ratio images is described, for example, in U.S. Pat. No. 4,949,167--Isnardi et al. In this system side panel image information is encoded by time compressing low frequency side panel luminance and chrominance information into horizontal overscan regions of a main panel component, and high frequency side panel luminance and chrominance information are encoded by time expansion and modulation of an auxiliary subcarrier.
The system disclosed in U.S. Pat. No. 4,949,167 employs intraframe signal processing at the transmitter and receiver. Intraframe processing is a signal processing technique which prepares two signals for mutual combining so that they can be recovered efficiently and accurately afterwards, such as by means of a field storage device. The type of signal processing employed for this purpose makes two signals identical on a field basis, i.e., by obtaining two samples with identical values one field (262H) apart. Intraframe averaging, a form of paired pixel processing, is one type of intraframe processing. In intraframe averaging pairs of fields are made identical by averaging pixels that are 262H apart, with the average value replacing the original values in each pair. This process occurs within a frame and does not cross frame boundaries.
In the system described in U.S. Pat. No. 4,949,167, intraframe averaging high frequency main and side panel information reduces the temporal update rate of these frequencies by half, i.e., to an update rate of 1/30 of a second, which is one-half of the normal field update rate of 1/60 of a second. The vertical resolution of these frequencies also is reduced in half. The reduced temporal update rate, particularly with respect to luminance frequencies, can result in perceived jerky motion, sometimes referred to as "judder", depending on the location of the frequency split point between the intraframe processed high frequencies, and the low frequencies which are not intraframe processed.
The frequency split point may be different for main panel and side panel intraframe processing for a variety of reasons relating to system signal processing requirements. For example, in the system of U.S. Pat. No. 4,949,167 the main panel information is intraframe processed above 1.5 MHz. Side panel high frequency information with a bandwidth of 700 KHz-5.0 MHz is time expanded to produce a side panel signal with a 1.16 MHz bandwidth, which is subjected to intraframe processing in its entirety. The different frequency split points of the main and side panels (1.5 MHz and 0.7 MHz) may produce a difference between the judder perceived in the main and side panels, i.e., "differential judder". Thus low frequencies not subject to intraframe processing are sent with a relatively "smooth" 60 Hz update rate, intraframe averaged high frequencies are sent with a 30 Hz update rate exhibiting judder, and main panel-side panel differential judder is likely to be perceived as noted above. The apparatus described herein in accordance with the principles of the present invention is directed to significantly reducing or eliminating the differential judder effect.